Field of the Invention
The present invention relates to a brewing device for an espresso maker, in particular a brewing device in which an amount of grounds introduced into a brewing chamber is controlled during each cycle in order to guarantee a repeatable result for a selected beverage type.
Description of Related Art
The amount of grounds to introduce into the brewing chamber can be alterable in order to obtain different beverages, specifically strong coffee known as ristretto, espresso, lungo, etc.
The brewing device of a coffee maker typically has a brewing chamber, which is supplied with grounds, and a pressing ram, which compresses the grounds in the brewing chamber into a cake. The grounds are generally produced by a coffee grinder equipped with grinding wheels, one of which is driven in rotation. The amount of grounds delivered corresponds to a grinding wheel drive time stored in a control circuit. However, several parameters, specifically the wear of the grinding wheels or the hardness of the coffee beans, can cause the amount of grounds delivered to vary even with the same grinding wheel drive time.
For measuring this variation, adding a device for measuring the thickness of the cake of compressed grounds, which is representative of the amount of grounds introduced into the brewing chamber, is known to the prior art. The thickness of the cake of grounds is calculated from the measurement of the compaction position of the pressing ram in the brewing chamber.
An appliance for preparing beverages having a brewing device comprising a brewing chamber which receives the grounds and a pressing rain which is axially displaced by an electric motor from a waiting position outside the chamber to a compaction position inside the chamber is thus known from document EP0627186. A sensor associated with a control device is used to calculate the compaction position of the rain in the chamber by counting the number of revolutions of the motor. The sensor can be a Hall effect sensor associated with several magnets driven in rotation or an optical sensor associated with a slotted disc driven in rotation by the motor. The compaction position of the rain can then be compared to a predetermined value, a deviation between these two values indicating the presence of too small or too large an amount of grounds in the chamber.
In this construction, however, the sensors and the associated movable elements are expensive and complicated and are a potential source of breakdowns. An optical sensor in particular is sensitive to fouling in the environment of an espresso maker.
Also known from document EP2394541 is a brewing device for an espresso maker having a brewing chamber for receiving grounds, a pressing ram mounted movably in translation along a path of travel extending between a top retracted position in which it is situated above the brewing chamber and a bottom compaction position in which it penetrates the brewing chamber to form a cake of compacted grounds, wherein the pressing ram is driven by a hydraulic drive mechanism with a hydraulic cylinder and a pump. The device has a rotary potentiometer controlled by drive means during the travel of the pressing ram, making it possible to measure the compaction position of the pressing rain and deduce the height of a cake of compacted grounds therefrom.
This document discloses a device for driving the pressing rain that is economical insofar as the pump supplying the hydraulic cylinder is necessary for the injection of hot water under pressure into the brewing chamber for making coffee. For measuring the height of the compacted cake of grounds, however, the potentiometer is an expensive and bulky component that is hard to fit in the brewing device.
The object of the present invention is to remedy the aforementioned disadvantages and to propose a brewing device enabling precise control of the amount of grounds introduced into a brewing chamber that is simple in design and inexpensive to implement.
Another object of the present invention is to propose a brewing device that operates in a reliable manner.